1. Field of the Invention
The present invention relates generally to:the field of microreactors and more particularly to a microfluidic device and a method of manufacturing such microfluidic devices.
2. Technical Background
Microfluidic devices are structures familiar to those skilled in the art, structures for which numerous applications have already been described, in particular in references such as: Microreaction Technology, 3rd International Conference on Microreaction Technology; edited by W. Ehrfeld, published by Springer-Verlag, Berlin (2000); and Micro-total Analysis Systems 2000, edited by A. Van Den Berg, W. Olthius, and P. Bergveld, published by Kluwer Ac Publishers (2000). Within such structures, in volumes that are small (having a characteristic dimension that generally lies in the range of 10 micrometers (μm) to 1000 μm), fluids are directed and/or mixed together and/or caused to react.
Such devices known in the art include, microfluidic devices made of various types of material, and in particular of polymers, of silicon, or of metals. The shortcomings encountered with those materials are numerous. For example, devices made of polymers cannot withstand temperatures of more than 200° C. to 300° C. over a prolonged period. Moreover, it is often difficult to control surface states effectively within such structures.
Silicon devices are expensive, incompatible with certain biological fluids, and the semiconductive nature of silicon gives rise to problems with implementing certain pumping techniques, such as electro-hydrodynamic pumping and electro-osmotic pumping.
Devices made of metal are liable to corrode, and in like manner they are typically not compatible with certain biological fluids.
It has therefore been found desirable, in numerous contexts, to have fluidic microstructures made of glass, glass ceramic, or ceramic. Those materials are particularly appreciated for their insulating nature (thus, U.S. Pat. No. 6,210,986 describes the benefit of having insulating structures available when the fluid is moved by electro-osmosis or by electrokinetics), for their resistance or even inertness in the face of chemical attack, for their transparency, for their surface homogeneity, and for the ease with which their surfaces can be modified chemically. Microfluidic devices made of glass have been obtained by chemical or physical etching. Those etching technologies give rise to hollows in a glass substrate and they are not entirely satisfactory to implement. Isotropic chemical etching does not enable significant aspect ratios to be obtained, while physical etching is difficult to implement, in particular because of its high cost and limited production capacity. To close such open structures, the technique most often employed is ionic attachment. That technique is expensive, and difficult to implement insofar as it is highly sensitive to dust and insofar as the surface of each layer that is to come into contact must be as flat as possible in order to provide high quality sealing.
Microfluidic devices made of ceramic, as described in European patent application No. EP-A-0 870 541, generally are obtained by ceramizing a stack of ceramizable layers (green mixture of ceramic powders and an organic binder). In the stack, there is no support layer, and within each ceramizable layer the empty volume remains limited.
In another context, that of screens and digital displays, the following techniques have been described. Generally speaking, glass forming operations to generate rectilinear parallel ribs on a flat support are known in the art. Unlike the method of the present invention, such forming steps are not performed in a vacuum. Known techniques are well represented in U.S. Pat. No. 5,853,446.
Operations for closing open plane structures having rectilinear parallel ribs, such as those obtained by the above-mentioned forming operations are also known. In accordance with such forming operations, a fine layer of glass paste is placed on these ribs, which are not too far apart. This is described in Japanese application No. JP-A-12 187 028. The technique incorporating the fine layer of glass cannot in any way be considered to be equivalent to the support substrate of devices made in accordance with the present invention.
What is needed therefore, but presently unavailable in the art, is a microfluidic device and method of manufacturing such a microfluidic device that overcomes these and other shortcomings associated with the use and manufacture of microfluidic devices known in the art. Such microfluidic devices should be capable of obtaining high aspect ratios, and should be well suited for use as microreactors for the chemical, pharmaceutical, and biotechnology industries. The method of manufacturing such microfluidic devices should be compatible with low cost production while at the same time provide advantageous yields. It is to the provision of such a microfluidic device and method of manufacturing such microfluidic devices that the present invention is primarily directed.